A material that changes color depending upon the light can be represented by a photochromic material. The photochromic material reversibly varies the structure depending upon the incidence of ultraviolet rays and has a property of exhibiting varying absorption spectrum. This is the property of a material in that if an isomer is irradiated with light of a particular wavelength, the single chemical material reversibly forms another isomer having a different absorption spectrum due to the action of light. The formed another isomer resumes the color of the initial isomer due to heat or light of another wavelength.
There have been proposed photochromic spectacles using lenses that have properties of the photochromic material. Outside of a house, the photochromic spectacles quickly develop a color being irradiated with light containing ultraviolet rays such as of sunlight and works as sunglasses. Inside of the house where no light is incident, the photochromic spectacles have its color faded and works as an ordinary transparent spectacles.
Lenses having photochromic properties have heretofore been produced by a method which lets the surfaces of the lenses without photochromic property soaked with a photochromic compound, a method of directly obtaining a photochromic lens by dissolving a photochromic compound in a monomer followed by polymerization, and a method of forming a layer having photochromic property on the surface of the lens by using a coating solution that contains a photochromic compound (coating method).
Among the above methods of producing lenses, the coating method comprises forming a coating on the surface of the lens by the spin coating by injecting, onto the surface of the lens, a coating solution from a nozzle of a container containing the photochromic coating solution while rotating the lens. An apparatus for continuously coating a plurality of lenses can be represented by, for example, a coating apparatus disclosed in a patent document 1 described below which is equipped with an auxiliary mechanism for spreading a coating solution on the lenses by using a flexible film.
In order to form a coating having a sufficient degree of photochromic properties by the coating method, a photochromic solution having a relatively high viscosity of, for example, 25 to 1000 centipoises (cP) at 25° C. must be uniformly applied maintaining a thickness of not less than 5 μm and, preferably, not less than 30 μm. Here, use of the above coating apparatus makes it possible to satisfy the above requirements by using the coating solution in small amounts.
There has further been proposed an apparatus for applying a photocurable coating solution onto the surfaces of the spectacle lenses and for photocuring the coating solution as taught in a patent document 2 though it is not a dedicated apparatus for applying the photochromic coating solution.
The coating solution-applying apparatus of the patent document 2 is provided with coating solution dripping means by which the surfaces to be coated of the spectacle lenses are arranged facing upward and the coating solution is dripped to coat the spectacle lenses. Further, the coating solution-applying apparatus is provided with a spatula mechanism which can be moved by a slide mechanism and with a holder 133 for holding a spatula 132. Referring to FIG. 15A, the spatula 132 intersects a horizontal line L that extends back and forth passing through the center O of a to-be-coated surface 131a and a given point P1 on the outer circumferential edge portion at a predetermined angle β. Therefore, the front end of the spatula 132 comes in contact with a point P2 which is separated away from the above given point P1 toward the rear side in the rotational direction by a distance Δ on the outer circumferential edge portion of the to-be-coated surface 131a. Referring to FIG. 15B, further, the spatula 132 is attached to the holder 133 so as to be tilted by a predetermined angle α in the axial direction of the spectacle lens 131 with respect to the vertical line. That is, the spatula 132 is arranged being tilted with respect to the horizontal line and the vertical line of the lens 131.
The spectacle lens 131 is provided on the side surface thereof with a pair of coating solution removing members 135 for smoothing the thickness of the coating solution adhered to the side surface 131b of the spectacle lens 131. The coating solution removing members 135 are made of a foamed resin (sponge) having excellent adsorbing property in a cylindrical shape, and are attached to the surfaces of the mounting plates of a pantagraph mechanism with their axes perpendicular thereto maintaining a predetermined gap in the back-and-forth direction, so as to be pushed with a predetermined force onto the side surface of the lens when extended.
In the coating solution-applying apparatus of the patent document 2 constituted as described above, coating solution dripping means 136 is, first, arranged on the outer circumferential surface side of the lens 131 as shown in FIG. 16A. To drip the coating solution, a nozzle 136a of the coating solution dripping means 136 is moved from the outer circumference toward the center of the spectacle lens 131 as shown in FIG. 16B and is driven and controlled so as to apply the coating solution onto the surface of the lens 131 in a spiral manner.
When the coating solution is applied onto the to-be-coated surface of the lens by the spin-coating method, the coating solution spreads over the whole to-be-coated surface due to the centrifugal force created by the rotation of the lens and partly scatters and drops. At the outer circumferential edge portion of the to-be-coated surface of the lens, further, the coating becomes thick and swells due to the surface tension. If the film is thick, wrinkles may occur when the coating is cured by being irradiated with ultraviolet rays in the step of curing which is the next step. Therefore, the spatula 132 is provided for smoothing the coating solution and for removing excess of the coating solution at the outer circumferential edge portion of the to-be-coated surface of the spectacle lens.
Further, if the front end of the spatula 132 remains contacted to the outer circumferential edge portion of the to-be-coated surface of the spectacle lens, the coating solution stays along the outer circumferential edge of the to-be-coated surface of the lens due to the rotation of the spectacle lens. According to the coating solution-applying apparatus of the patent document 2, therefore, after the coating solution is dripped, the spatula 132 is arranged at the upper edge on the side surface of the lens 131 being tilted in the horizontal direction and in the vertical direction, and the coating solution removing member 135 is arranged on the side surface of the lens 131 as shown in FIG. 16C. An excess of the coating solution can be removed by the spatula 132, and the coating solution can be smoothed. According to the patent document 2, further, the coating solution dripped on the side surface 131b of the lens 131 is thinly spread so as to form a uniform coating of a uniform thickness by pushing the coating solution removing member 135 onto the side surface 132a of the spectacle lens 131.
Patent document 1: JP-A-2005-13873
Patent document 2: JP-A-2005-246267